Charm estimate from the dilepton spectra in nuclear collisions

The validity of a recent estimate of an upper limit of charm production in central Pb+Pb collisions at 158 A GeV is critically discussed. Within a simple model we study properties of the background subtraction procedure used for an extraction of the charm signal from the analysis of dilepton spectra. We demonstrate that a production asymmetry between positively and negatively charged background muons and a large multiplicity of signal pairs can lead to biased results. Therefore, the applicability of this procedure for the analysis of nucleus-nucleus data should be reconsidered before final conclusions on the upper limit estimate of charm production can be drawn. (6 refs).